NCERT Class 9 Science (Chemistry) Chapter 1 – Matter in Our Surroundings

The following substances are matter:

Chair

Air

Almonds

Lemon water

The smell of perfume (Smell is considered as a matter due to the presence of some volatile substances in air that occupy space & have mass.)

Particles in the air, if fueled with higher temperatures, acquire high kinetic energy, which aids them to move fast over a stretch. Hence, the smell of hot sizzling food reaches a person even at a distance of several meters.

The diver is able to easily cut through the water in the swimming pool because of the weak forces of attraction between water molecules. It is this property of water that attributes to easy diving.

The characteristics of particles of matter are as follows:

(a) Presence of intermolecular spaces between particles

(b) Particles are in constant motion

(c) They attract each other

(d) All matter is composed of very small particles which can exist independently.

The following substances are arranged in increasing density:

Air

Exhaust from chimney

Cotton

Water

Honey

Chalk

Iron

(a) The difference in the characteristics of the three states of matter.

(b) (i) Rigidity: It is the property of matter to continue to remain in its shape when treated

with an external force.

(ii) Compressibility: It is the attribute of the particles to contract their intermolecular space when

exposed to an external force, thereby escalating its density.

(iii) Fluidity: It is the ability of a substance to flow or move about freely.

(iv) Filling the gas container: The particles in a container take their shape as they randomly vibrate in all possible directions.

(v) Shape: It is the definite structure of an object within an external boundary

(vi) Kinetic energy: Motion allows particles to possess energy which is referred to as kinetic energy. The increasing order of kinetic energy possessed by various states of matter are:

Solids < Liquids < Gases

Mathematically, it can be expressed as K.E = 1/2 mv2, where ‘m’ is the mass and ‘v’ is the velocity of the particle.

(vii) Density: It is the mass of a unit volume of a substance. It is expressed as:

d = M/V, where ‘d’ is the density, ‘M’ is the mass and ‘V’ is the volume of the substance

(a) There is a low force of attraction between gas particles. The particles in the filled vessel are free to move about.

(b) Gaseous particles have the weakest attraction force. They are always moving in a haphazard manner. When a gas particle collides with the container’s walls, it exerts force and, thus pressure on the wall.

(c) There is a distinct contour and volume to the hardwood table. The wood particles are tightly packed. They do not conform to the container’s shape. As a result, the solid features of a hardwood table are satisfied.

(d) The boundaries between air particles are quite loose. They are a long way apart and have a lot of space between them. As a result, we may move our hands freely in the air. The particles in a solid block, on the other hand, are bound together by a strong force of attraction. As a result, there is either some or no space between them. As a result, we will require a karate expert.

In general, the volume of a liquid is more than the volume of a solid because liquid particles are freer to move, resulting in more volume. Ice, on the other hand, has a maximum density of water at 4 degrees Celsius. Ice is lighter than water and has a lower density. As a result, it floats on water.

a.  0°C=273K

300K= (300-273)°C = 27°C

b. 573K= (573-273)°C = 300°C

(a) At 250°C – Gaseous state since it is beyond its boiling point.

(b) At 100°C – It is at the transition state as the water is at its boiling point. Hence it would be present in both liquid and gaseous states.

It is due to the latent heat as the heat supplied to increase the temperature of the substance is used up to transform the state of matter of the substance; hence, the temperature stays constant.

It can be achieved by either increasing the pressure or decreasing the temperature, which ultimately leads to the reduction of spaces between molecules.

It is because the temperature is high and less humid on a hot dry day, enabling better evaporation. High levels of this evaporation provide better cooling effects.

An earthen pot is porous in nature. These tiny pores facilitate the penetration of water and hence their evaporation from the pot surface. The process of evaporation requires energy which is contributed by water in the pot as a result of which water turns cooler.

Acetone, petrol, and perfume are volatile substances that evaporate when they come in contact with air. Evaporation is facilitated as it uses energy from the palm, hence leaving a cooling effect on our palms.

A saucer has a larger surface area than a cup, promoting quicker evaporation. Hence, the tea or milk in a saucer cools down faster.

In summer, it is preferred to wear light-coloured cotton clothes because light colour reflects heat and cotton materials have pores that absorb sweat, facilitating evaporation, and hence causing a cooling effect on the skin.

0°C=273K

(a) 293K= (293 – 273)°C = 20°C

(b)  470K= (470 – 273)°C = 197°C

0°C = 273K

(a) 25°C = (25+273)K = 298K

(b) 373°C = (373+273)K = 646K

(a) At room temperature, naphthalene balls undergo sublimation wherein they directly get converted from a solid to a gaseous state without having to undergo the intermediate state, i.e., the liquid state.

(b) Molecules of air move at a higher speed and have large intermolecular spaces. Perfumes comprise substances that are volatile, which scatter quickly in air, becoming less concentrated over a distance. Hence, we are able to smell perfume sitting several metres away.

Oxygen (gas) < water (liquid) < sugar (solid)

(a) At 25°C, the water will be in liquid form (normal room temperature)

(b) At 0°C, the water is at its freezing point, hence both solid and liquid phases are observed.

(c) At 100°C, the water is at its boiling point, hence both liquid and gaseous states of water (water vapour) are observed.

(a) Water persists as a liquid at room temperature since its melting point is lower than room temperature and its boiling point (100o C) is higher. 

Similarly,

(i). A fixed volume is occupied by a fixed mass of water.

(ii). At room temperature, water does not have a fixed shape and flows to fit the container’s shape.

As a result, water is a liquid at room temperature.

(b) Because its melting and boiling points are above room temperature, an iron almirah is a solid at room temperature. In the same way, 

(i) An iron almirah is rigid and has a predetermined shape.

(ii) Metals have a relatively high density.

As a result, at room temperature, iron almirah is a solid.

At 273 K, ice will absorb heat energy or latent heat from the medium to overcome fusion and transform into water. As a result, ice has a greater cooling impact than water at the same temperature since water does not absorb the excess heat from the medium.

Steam produces severe burns. It is because it is an exothermic reaction that releases a high amount of heat which it had consumed during vaporization.

Interconversion of three states of matter: Using temperature or pressure, any state of matter can be turned into another.

(A) Solid to Liquid → Melting (or) fusion (or) liquefaction

(B) Liquid to Gas → Evaporation (or) vaporization

(C) Gas to liquid → Condensation

(D) Liquid to Solid → Solidification

(E) Solid to Gas → Sublimation

(F) Gas to Solid → solidification